1. Field of the Invention
The present invention relates to a keyless entry device having a tire pressure monitoring function, and more particularly to a keyless entry device having a tire pressure monitoring function whose operation is changed over between an operation as a tire pressure monitoring device and an operation as a keyless entry device in an interlocking manner with turning on and off of an ignition key of an automobile.
2. Description of the Related Art
Conventionally, as devices mounted on an automobile, there have been known a keyless entry device and a tire pressure monitoring device. To describe the constructions of these devices, the keyless entry device includes a vehicle-mounted transmission/reception unit which is mounted on the automobile and one or more portable transmission/reception units which an owner or the like individually carries. When a normal high frequency signal is transmitted from the portable transmission/reception unit and the vehicle-mounted transmission/reception unit receives the high frequency signal, opening/closing of an automobile door is performed or starting of an engine is performed. On the other hand, the tire pressure monitoring device includes a vehicle-mounted receiver which is mounted on an automobile and a plurality of small transmitters which are mounted on respective tires, wherein when a normal high frequency signal of equal to or more than a fixed level is transmitted from a plurality of small transmitters and the vehicle-mounted receiver receives the high frequency signal, the abnormality of air pressure or the abnormality of tire temperature of specific tires can be detected.
The above-mentioned known keyless entry device performs only functions peculiar to the keyless entry device, that is, opening/closing of an automobile door or starting of an engine without using a key by manipulating the portable transmission/reception unit. On the other hand, the above-mentioned known tire pressure monitoring device performs only functions peculiar to the tire pressure monitoring device, that is, detecting of the abnormality of air pressure of specific tires and the abnormality of tire temperature and the activation of an alarm when the abnormality is detected. Accordingly, to achieve both of the function of the keyless entry device and the function of the tire pressure monitoring device, it is indispensable to separately mount the keyless entry device and the tire pressure monitoring device on the vehicle.
On the other hand, inside the automobile, usually, various types of driving manipulation members and measuring equipment such as meters which are considered to be necessary for driving are arranged so that there is no tolerance in space. Accordingly, when the keyless entry device and the tire pressure monitoring device are separately mounted, it is rather difficult to select their mounting positions. Furthermore, when two devices consisting of the keyless entry device and the tire pressure monitoring device are individually mounted on the automobile, this surely pushes up the cost considerably.